State-to-state photodissociation dynamics of CO at 157 nm.

State-to-state photodissociation of CO( = 0 and 1) at 157 nm the O(D) + CO(Σ) channel was studied by using the sliced velocity map imaging technique. Both the O(D) and CO(Σ) products were detected by (2 + 1) resonance enhanced multiphoton ionization (REMPI). Detection of CO the Σ ←← Σ transition allowed ro-vibrational state-selective detection, and combined with imaging, the fragment energy and angular distributions have been derived. For CO( = 0 and 1|) products from the CO( = 0) molecule, the angular distributions of low- CO display positive anisotropic parameters (about 0.8); with increasing, the product anisotropic parameters gradually reduce to zero. While for CO( = 0 and 1|) products from the vibrational excited CO( = 1) molecule, the angular distributions of low- CO also display positive anisotropic parameters; with increasing, the product anisotropic parameters first decrease to zero and then become negative (about -0.5). Experimental results show that the observed variation of the product angular distribution with the rotational quantum number of CO is consistent with trends predicted by a classical model for non-axial fragment recoil. The results support advanced theoretical predictions of a predominantly parallel transition to the bent 2A' excited state of CO, where bending introduces torque during the direct dissociation process.